Thousands rallied in northern Japan calling for the G8 rich industrialised nations to be disbanded on Saturday while in Paris, member France called for the group to grow to include major emerging states such as China and India.
In Sapporo, several thousand people protested against the annual Group of Eight summit due to take place at a luxury hotel 70 km (45 miles) away.
The 90-minute march by Japanese and foreign activists took place under heavy security ahead of the July 7-9 meeting at the hot spring and lake resort of Toyako.
The protesters banged drums and carried colourful banners proclaiming "Shut Down the G8" and yelled: "We are against a summit of rich nations".
In Paris, French President Nicolas Sarkozy called for the meeting to include China and India as well as representatives from Latin America, Africa and the Middle East, saying the world today was "multipolar".
"I think it is not reasonable to continue to meet as eight to solve the big questions of the world, forgetting China -- 1 billion, 300 million people -- and not inviting India -- 1 billion people," he told a conference of the ruling UMP party.
The G8 includes the United States, Britain, Canada, France, Germany, Italy, Japan and Russia.
A SEAT FOR AFRICA
"The truth is that if we want peace and world development, everybody needs to be invited," Sarkozy said.
"I do not accept that a continent of 1 billion people like Africa does not have a country to represent it at the table of world leaders."
Sarkozy has said more than once that he thinks the group should be expanded. He did not detail on Saturday how the structure should be changed, however.
This year's G8 host, Japan, argues that the current size works well, with other countries brought into the group for discussions on specific issues. In all, 22 leaders are attending next week's meetings in Hokkaido.
"We cherish this format for G8," a senior Japanese government official told reporters this week, adding that the G8 countries "share common values".
The G8 nations will meet eight other countries, including China, India and Brazil, in an expanded Major Economies Meeting (MEM) on July 9 to look at long-term targets for climate change.
Environmentalists are urging the G8 to set bold targets for cutting C02 emissions by 2050 and interim goals for how to get there in order to boost momentum for U.N.-led talks on a new framework for after the Kyoto Protocol expires in 2012.
Those talks are set to end in Copenhagen next year.
"Countries like China and India also have to contribute to global efforts on cutting emissions, but ambitious mid-term targets by industrialsed nations are a crucial prerequisite," Kathrin Guttman, WWF International Climate Policy Coordinator, said in a statement.
"Rather than passing the buck to those countries less capable, the world's eight wealthiest nations should do what all real leaders do -- move first."
Japanese Prime Minister Yasuo Fukuda would like to make climate change a centrepiece of the summit, but divisions within the G8 and between rich and poorer countries over how to share the burden of reducing the greenhouse gases that cause global warming have cast doubt on how much the leaders can achieve.
African leaders will join the group for one day to discuss pledges made in a summit in 2005 to double aid to the continent by 2010, though the issue may be pushed down the agenda by a focus on surging food and oil prices and economic worries.
MAGNET FOR PROTESTS
Summits of the G8 have become a magnet for protesters angry about everything from climate change to the effects of globalisation.
In Saturday's protests, four Japanese men were arrested for violating the public safety ordinances or interfering with police activities, said a police official on the island of Hokkaido, of which Sapporo is the capital. A Reuters Video News cameraman was among those detained by police.
The protesters banged drums, carried colourful banners and yelled: "We are against a summit of rich nations".
A police source estimated the crowd at 2,000 to 3,000.
Many of the participants tried to keep it light, dressing in festival clothes, clown and animal costumes.
"Cats are against the G8 too", read one large cat-shaped placard.
"The G8 are very lazy kings," said Eugene Benoit, who came from France with the group No Vox, which works with the unemployed and people without papers. "They are working for the free market and not for the people."
The G8 was started in 1975 in the wake of the first oil crisis as an informal gathering of senior financial officials from the world's largest economies to discuss global problems.
The forum initially included the United States, Germany, France, Japan, Britain and Italy.
Canada joined a year later in 1976, making it the G7. Russia was invited to join after the collapse of the Soviet Union in 1991 and formally became a member in 1997.